1. Field of the Invention
The present invention relates to a process of a circuit board, and in particularly, relates to a surface treatment process for a circuit board.
2. Description of Related Art
In recent years, along with the progressive development of electronic technology and improvement of high-tech electronic industries, more humanistic electronic products with better functions are continuously put forward and progress towards “light, thin, short, and small.” Under such a trend, circuit boards having advantages of closed wiring, compact assembly, and good performance have become a main medium for carrying and electrically connecting a plurality of electronic components, in which the electronic components may be chips.
A flip-chip assembly is one of the methods for assembling a chip and a circuit board. The circuit board has a plurality of pads, and may be electrically and structurally connected to a chip by means of reflow of solder on the pads. In recent years, since more and more signals need be transmitted between electronic components (e.g. chips), the circuit board needs more pads. However, the circuit board has a limited space, so the pitch between the pads is developed towards the fine pitch.
FIG. 1 is a cross-sectional view of a conventional circuit board. Referring to FIG. 1, in the conventional art, usually, an oxidation protection layer 120 is formed on pads 112 of a circuit layer 110 of a circuit board 100 by electroplating. Subsequently, the black oxidation process is performed to form a black oxide layer 140 on the circuit layer 110 exposed by a solder mask layer 130 and the oxidation protection layer 120, so as to achieve the solder protection effects. The thickness of the oxidation protection layer 120 is in a range of 5 μm to 7 μm, and the thickness of the black oxide layer 140 is in a range of 1 μm to 3 μm. Therefore, the oxidation protection layer 120 protrudes from a surface 142 of the black oxide layer 140. Then, the solder (not shown) is disposed on the pads 112, and the circuit board 100 and the chip (not shown) are electrically and structurally connected by means of reflow of the solder (or flux) therebetween. However, when the solder is disposed on the pads 112 and bonded with the chip by means of reflow, the solder may be melted by heat and extruded by the protruding oxidation protection layer 120 and the chip, thus overflowing to the adjacent pads 112 to cause the short circuit of the pads 112.